The Aurora Borealis, affectionately known as the Northern Lights, put on a spectacular show over the Northumberland coast on Monday night, and experienced skywatchers from the Kielder Observatory called it "the best display in years."

By the time you read this it will be morning. Last night, well 1 am we had the best #aurora display in years...pics to come

The Northern Lights are caused by charged particles, usually electrons and protons, entering the atmosphere from above. This causes the ionization and excitation of other particles in the atmosphere, which in turn causes the emission of colored light. They most commonly appear green, but at very high altitudes can appear red and at lower altitudes appear blue.

On Monday night, the phenomenon occurred over Dunstanburgh Castle in the UK, and was visible not only to astronomers, but to the naked eye of passersby for several hours.

Here is a time lapse of the spectacle from Kielder Observatory:

"There was a small show around 10pm, then it got stronger after midnight and at 2am it went crazy," said Associated Press photographer Owen Humphreys. "There were a lot of greens and some pink colors in the sky. There were swirling and dancing pillars of light going 100ft in the air. It was unreal and the best show I have seen for years."

Here are some of the best pictures of the Northern Lights over Northumberland on Monday night: